Planes are not only to carry passengers, but they are also loaded with luggage belonging to the passengers. The planes are waiting to be loaded. You arrive at your destination and wait at the conveyer belt to remove your luggage that was on the plane. I remember once waiting and everyone had picked up their luggage and there was nothing left, but I did not have my case. This was quite annoying of course. Apparently instead of my case being sent to London from Zürich, it had arrived somewhere in Portugal. Eventually I got my luggage a day later, after being sent from Portugal to London, delivered by a truck to where I was staying at my friends house. Luckily my friend had given me a few items to wear until it arrived. My case had become a stowaway on another plane.